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Mihai Miclaus. Regulation of gene expression during maize endosperm development. 2011.

Abstract: Multigenic traits are very common in plants and cause diversity. Nutritional quality is such a trait and one of its factors is the composition and relative expression of storage protein genes, known as zeins in maize. They represent a medium-size gene family distributed over several chromosomes and unlinked locations. Two inbreds were selected to analyze allelic and non-allelic variability among the alpha-zeins. Genes were copied to unlinked sites before and after allotetraploidization of maize, but before transposition enlarged intergenic regions in a haplotype specific manner. Once genes were copied, expression of donor genes was reduced relative to new copies. Epigenetic regulation appeared to have contributed to silencing older copies because some of them could be reactivated when endosperm was maintained as cultured cells. Bisulfite sequencing of the promoter region also showed distinct methylation patterns of separate gene clusters as well as different tissues, possibly reflecting position effects on regulatory mechanisms as a result of inserting copies at unlinked locations.
Seed mutants with non-vitreous endosperm play an important role in the regulation of alpha-zein gene expression. Although a number of genes affecting endosperm vitreousness have already been isolated, it has been difficult to clone opaque7 (o7) – the last in the series of three high-lysine corn mutants – mainly because of its low penetrance in many genetic backgrounds. To overcome these difficulties, a combination of map-based cloning and transposon tagging was undertaken. An o7 candidate gene based on map position contained a 12-bp deletion in the second exon of an acyl-CoA synthetate (ACS)-like gene. A second allele was generated by transposon tagging, with a Dissociation (Ds) element inserting ~500 bp downstream of the deletion, in the same exon. Although zein synthesis appeared to be unaltered in o7-ref and protein accumulation changed only slightly, PBs exhibited striking membrane invaginations. A plausible model consistent with these observations is that the ACS enzyme plays a key role in membrane biogenesis and that altered PBs render the seed non-vitreous.

Keywords: zein, epiregulation, gene expression, haplotypes, maize, opaque7, acyl-CoA, transposon-tagging, map-based cloning

Posted by Mihai Miclăuş

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